1. Field of the Invention
The present invention relates to alkylamino/imino Benz-iso-Quinoline derivatives that are useful as fluorescent leak detection dyes in lubricants.
2. Description of the Related Art
Derivatives of 1H-Benz(de)isoquinoline-1,3(2H)-diones, sometimes named as 1,8-naphthalimides, have been known for some time (See for example U.S. Pat. Nos. 2,006,017 and 2,385,106) and are mainly utilized either as optical brightening agents or bright fluorescent yellow dyes applied to natural and man-made textile fibers. In all these applications the compounds are required to possess some degree of water solubility. Water-insoluble compounds have also been proposed as fluorescent dyes for certain thermoplastics, for example, polystyrene and for imparting fluorescent effects to petroleum hydrocarbon based fuels and lubricants, either for aesthetic reasons or for detecting leakage of fluid. An example of the latter usage is described in U.S. Pat. No. 4,758,366. When a leak occurs, the dye present in the lubricant composition is deposited on the area of the container surrounding the leak. Upon exposure to long wave ultraviolet light, also called "black light", the dye fluoresces. By irradiating the exterior of the container, a leak and its location can be visually determined by the fluorescent response. Such a method is generally convenient for determining the presence and location of small leaks.
This type of method has become especially valuable in detecting refrigerant fluid leaks from automobile, domestic, and industrial air conditioning and refrigeration systems, since such a leak implies the loss of halogenated refrigerant gas. Escape of these types of gases is of primary environmental concern due to the possible damage they do to the ultraviolet light absorbing ozone gas layer of the earth's upper atmosphere. The dye which has almost entirely dominated this technique in commercial practice is N-butyl-4-butylamino-1,8-naphthalimide, a compound named by Chemical Abstracts Services as 1H-Benzde!isoquinoline-1,3(2H)dione, 2-butyl-6-(butylamino) and identified by the "Colour Index" system of classification as C.I. Solvent Yellow 43 (hereinafter referred to as "Solvent Yellow 43"). This compound is a dry powder dye with a melting point of 127.degree. C. It has a comparatively low direct solubility, not exceeding 1% in contemporary hydrocarbon based refrigerant oils, and less in the more recently developed refrigerant lubricants such as polyalkylene glycols and their esters. Because of its low direct solubility in the refrigerant oils, and the inconvenience of handling dry powder dye in an engineering plant, Solvent Yellow 43 is normally supplied as a pourable, but viscous, concentrate solution that contains up to 20% by weight of the dye in an organic solvent such as aromatic hydrocarbons. These concentrates are relatively clean to handle and can be diluted directly into the refrigerant oils.
However, the development of new lubricants, which are adapted to be miscible with the now required non-CFC refrigerants, has caused a problem with the use of Solvent Yellow 43. Specifically, Solvent Yellow 43 tends to crystallize out of these lubricant compositions during use. The precipitated crystals can clog various portions of the refrigeration equipment, such as the fine jets, thereby causing a shut down of the system. Accordingly, Solvent Yellow 43 is not practically employed in the new type of refrigerant lubricants.
Another dye proposed for leak detection in refrigerant compositions is apparently N-(iso)nonyl4-(iso)nonylamino-1,8-naphthalimide. This dye, like Solvent Yellow 43, is quite acceptable when used with conventional lubricants such as mineral oil, but, is problematic when used in the newer types of lubricants. The dye can precipitate out as a tarry mass during use due to the absorption of small amounts of water by the refrigerant lubricant, especially those based on the newer polyalkylene glycol ester type oil. Consequently, this dye is not a practical alternative to Solvent Yellow 43 in the newer refrigerant lubricants.
Accordingly, there is a demand for a fluorescent dye that is compatible with a wide variety of lubricant compositions and oils and which will not crystallize or otherwise fall out of solution over a wide range of operating temperatures, durations, and conditions. The present invention provides fluorescent dye compounds and lubricant compositions for a refrigerant that enables fluorescent leak detection. Fluorescent dyes of the present invention, moreover, do not require aromatic hydrocarbons or other cosolvents in order to be incorporated into a lubricant composition.